Electrical cable for heavy currents



May 31, 1960 H. HORN ELECTRICAL CABLE FOR HEAVY CURRENTS Filed Nov. 26,1954 GLASS RIBBON ELECTRIC CONDUCTOR METALLIC SHEATH METAL THREADSHEAT-SENSITIVE INSULATION INSULATING COMPOUND POROUS IMPREGNATEDELEC'I'RICALLY CONDUCTIVE LAYER INVENTOR. H EI N Z HO I? N %-m Nut 41,

QT'TORNEYS heat-protection,

United m Patent 1 1 .Germany,' a corporation of Germany Fi'led No'v.'26, 1954, seam. 471,443

4 Claims. (Cl. 174--102) This invention relates to electrical cable ofthe type having an impregnated paper or other heat-sensitive insulationsurrounding the conductor and which, in turn, is surrounded "by aprotective aluminum sheath. The invention has particular reference to animproved cable of this character provided with a heat protecting layerbetween the aluminum sheath and the heat-sensitive insulation to protectthe latter from high temperatures occurring during application of thesheath to the cable.

In the manufacturev of electrical cable having an aluminum sheath, theusual practice is to extrude or press the aluminum around the cable corecomprising the conductor and insulation. Due to the high temperaturesencountered in thus applying the aluminum, some provision must be madeto protect the underlying core from damage by the heat, particularly atthose regions of the cable length where the sheath press or extruder isstopped to introduce a new charge of aluminum into the container, thatis, at the regions of the so-called stops. Heretofore, variousexpedients have been used to provide this one of which is a simple heatprotection layer of heat-resisting material, such as asbestos, fineglass, or the like. To increase the heat protection, however, it hasalso been proposed to provide a double heatprotective layer arranged onthe cable insulation in the regions of the stops, this layer consistingof a wrapping of metal ribbon or metallized paper ribbon arrangeddirectly around the cable core, and a wrapping of glass ribbonsurrounding the first ribbon. In order to relieve electrically theprotecting layer of glass ribbon, which is not impregnated with the oilor other impregnator of the cable insulation, the underlying metallicwrapping may be electrically connected at intervals with the metalsheath of the cable. As an alternative, it has also been proposed towrap the cable core with a metallized paper ribbon folded at the edge toform a heat-insulating air space between the cable sheath and the cablecore, the metallized part of the ribbon lying on the outside so that itis in electrical contact with the metal sheath of the cable, whereby theheat insulating space is kept free from electrical charge. Both of thesearrangements have the disadvantage that one of the heat-protectinglayers is always filled at least partly with air, which allows migrationof the oil or other impregnator from the insulation into theheat-protection layer. This migration may in time cause a depletion ofthe impregnator in the insulation, or it may cause a deterioration ofthe impregnator due to chemical reaction between the impregnator and theoxygen in the heat-protective layer.

The present invention has for its principal object the provision of animproved cable of the character described having a heat-protectingarrangement which avoids the above-noted disadvantages.

A cable made according to the invention comprises a porous, electricallyconductive layer, which is preferably of carbon black paper, arrangeddirectly around the cable core, and a layer of glass ribbonarrangedaround the free of electrical charge; and

2,938,943 Patented May 31, 1960 ICC layer of carbon black paper or thelike, and located underneath'the aluminum sheath of the cable, the glassribbon layer being interlaced with copper or other metal threads toinsurean electrical connection with the porous conductive layer. Withthis construction, the heat protecting layer consisting essentially offine glass is kept the electrically conductive layer sealing the cablecore, due to its porosity, is permeable to the impregnator of the cableinsulation and, therefore, may be impregnated simultaneously with thecable core. Thus, deterioration of -the impregnator through contact withair in the finished sheath cable is avoided. At the same time, theheatprotective layer filled with impregnator may serve as a reservoirfor the impregnator during temperature changes of the cable.

For a better understanding of the invention, reference may be had to theaccompanying drawing in which the single illustration is across-sectional view of a preferred form of the new heavy-current cable.

Referring to the drawing, the cable as there shown comprises a pluralityof conductors 1, each of which is surrounded by insulation 2. Theinsulation 2 may be of any suitable material, but is preferably paperwrapped around the conductor and impregnated with oil. The wedge-shapedspaces between the insulated conductors are filled with a suitableinsulating compound 3, such as any of the compounds conventionally usedfor this purpose. The cable core thus formed by the parts 1, 2 and 3 iswrapped with carbon black paper forming a porous electrically-conductivelayer 4. A layer of glass ribbon 5 is wrapped around the layer of carbonblack paper 4, and the glass ribbon layer 5 is interlaced with copperthreads 6. These copper threads are embedded in'the glass ribbon layer 5and are exposed at the opposite faces of this layer. The glass ribbonmaking up the layer 5 may be of the conventional fiber-glass type,except for the addition of the copper threads 6 with which the glassfibers are interlaced or interwoven.

The protective aluminum sheath 7 is pressed or extruded around the glassribbon layer 5.

It will be apparent that the carbon black paper 4 forms a non-metallicporous layer which is electrically conductive and is wrapped directly onthe cable core. Because of the porosity of the layer 4, the cable coremay be impregnated with the oil or other impregnator after the layer 4has been applied, so that the cable core and the conductive sealinglayer 4 are impregnated simultaneously. Thereafter, the glass ribbonlayer 5 may be wrapped around the layer 4, followed by pressing orextruding of the aluminum sheath 7 over the glass ribbon layer. Thecopper threads 6 which interlace the glass ribbon layer 5 serve to forman electrical connection between the aluminum sheath 7 and the layer 4of carbon black paper.

In the preferred construction, along the entire length of the cablebetween the underlying core and the overlying aluminum sheath. However,in some cases it may sutfice to arrange these layers 4-5 only in theregions of the stops of the aluminum sheath, where there is the greatestneed for heat-protection of the underlying cable core. Accordingly, theappended claims are not to be construed as limiting the invention to anarrangement in which the heat-protecting layer extends over the wholelength of the cable.

I claim:

1. In a heavy-current electrical cable having a cable core including aconductor and a heat-sensitive insulation surrounding the conductor, anda protective metallic sheath surrounding the cable core, the improvementwhich comprises a porous, impregnated electrically-conductive layerinterposed between the cable core and the the layers 4 and 5 extendsheath, a layer of glass ribbon wrapped around said porous conductivelayer between said last layer and the sheath, and metallic threadsinterlacing the glass ribbon layer and providing an electricalconnection between said impregnated porous conductive layer and thesheath.

2. The improvement according to claim 1, in which said porous conductivelayer is carbon black paper.

3. The improvement according to claim 1, in which said threads arecopper threads embedded in the glass ribbon layer.

4. The improvement according to claim 1, in which said heat-sensitiveinsulation is impregnated paper, said porous layer being impregnatedwith the impregnator of said insulation.

References Cited in the file of this patent UNITED STATES PATENTS AimeNov. 1, 1938 Jacob Aug. 7, 1945 Rasero Dec. 23, 1947 Beaver Oct. 24,1950 Holmes July 15, 1952 FOREIGN PATENTS Great Britain Mar. 30, 1936Great Britain Feb. 10, 1943 Germany July 8, 1949

